The polyphenylene ethers and processes for their preparation are well known in the art. They are described in Hay, U.S. Pat. No. 3,306,874 and U.S. Pat. No. 3,306,875 and Blanchard et al, U.S. Pat. NO. 3,219,625 and U.S. Pat. No. 3,219,626 all of which are incorporated by reference. Other patents which show the preparation of polyphenylene ethers include Price et al, U.S. Pat. No. 3,382,212 and Kobayashi et al, U.S. Pat. No. 3,455,880 which are also incorporated by reference.
The processes most generally used to produce the polyphenylene ethers involve the self-condensation of a monovalent phenol in the presence of an oxygen-containing gas and a catalyst comprising a metal-amine complex.
These processes are carried out in the presence of an organic solvent and the reaction is usually terminated by removal of the catalyst from the reaction mixture.
Aqueous solutions of acids such as acetic acid, hydrochloric acid, and sulfuric acid, are generally the most efficient means of removing both the metal and amine components of catalyst residues of polyphenylene ether reactions. Organic acids, such as acetic acid, however, are less desirable for this purpose because of their relatively high cost and the difficulties involved in either disposing of them (environmental concern) or recovering them for reuse. Hydrochloric acid and sulfuric acid on the other hand, while less costly and more easily disposed of, are difficult to use because of their corrosive nature and because of their effects on the polyphenylene ether properties.
Use of hydrochloric acid generally results in incorporation of residual chloride in the polyphenylene ether which results in poor oxidative stability of the polymer.
Use of the aqueous solutions of sulfuric acid for extraction of copper-amine catalyst residues causes formation of emulsions with polyphenylene ether solutions which are difficult to separate. Sulfuric acid also is known to cause sulfonation of polyphenylene ethers. Were it not for these problems, and the problem of equipment corrosion, sulfuric acid would be a very attractive extraction agent for catalyst residues.
Chelating agents have also been employed for extraction of copper-amine catalyst residues. These materials are relatively efficient, but they are expensive and problems are encountered in the separation of residues for disposal purposes.
It has now been found that the use of bisulfate salt solutions in place of sulfuric acid eliminates these problems and permits efficient extraction of catalyst residue. Bisulfates are much less corrosive to stainless steel. (Samples of Carpenter type 316L Ht 46626 stainless steel in 10% sulfuric acid at 212.degree. F showed 77% weight loss in 28 days, whereas the same material in 10% sodium bisulfate at 212.degree. F showed only 3.8% weight loss in 29 days). The bisulfate solutions usually do not form emulsions with polyphenylene ether solutions, thus allowing easier phase separation. Also they are efficient in extracting the complex copper-amine catalyst.
Accordingly, it is a primary object of the present invention to provide an efficient process for separating a catalyst residue of polyphenylene ether resin from its reaction mixture which employs inexpensive relatively non-corrosive reagents.